Astronomy Picture of the Day

Explanation: Blown by the wind from a star, this tantalizing, ghostly apparition is catalogued as NGC 7635, but known simply as The Bubble Nebula. Astronomer Ken Crawford's striking view combines a long exposure through a hydrogen alpha filter with colour images to reveal the intricate details of this cosmic bubble and its environment. Although it looks delicate, the 10 light-year diameter bubble offers evidence of violent processes at work. Seen here above and left of the Bubble's centre is a bright hot star embedded in telltale blue hues characteristic of dust reflected starlight. A fierce stellar wind and intense radiation from the star, which likely has a mass 10 to 20 times that of the Sun, has blasted out the structure of glowing gas against denser material in a surrounding molecular cloud. The intriguing Bubble Nebula lies a mere 11,000 light-years away toward the boastful constellation Cassiopeia.